1. Field of the Invention
The present invention relates to a method for manufacturing a double-sided wiring glass substrate. Particularly, the present invention relates to a method for manufacturing a double-sided wiring glass substrate having on the front and rear surfaces thereof wirings and capable of mounting thereon various electronic parts.
2. Description of the Related Art
In recent years, there has been rapidly developed a MEMS (Micro Electro Mechanical System) in which function elements such as a sensor or a switch are constituted on a chip using an IC manufacturing technology, and as a result, dramatic miniaturization and high performance of electronic parts are being realized. In keeping with this trend, there is desired a wiring substrate capable of densely mounting with high reliability at low cost various conventional electronic parts and other electronic parts (hereinafter, referred to as “electronic parts”) using the MEMS.
Conventionally, there is known a wiring substrate using as a core substrate material thereof a ceramic substrate, a glass epoxy substrate or a glass substrate. Particularly, in the case of the glass substrate, many photosensitive glass substrates capable of forming a hole or a groove using a photolithographic method are used. An example of the wiring substrate using the photosensitive glass substrate includes a multilayer wiring substrate (see, Japanese Unexamined Patent Application Publication No. Sho 63-128699 (p4, column 2, lines 6 to 19)). The multilayer wiring substrate is formed as follows. That is, a through-hole or wiring groove formed in the photosensitive glass substrate using the photolithographic method is filled with conductive paste by a screen printing method to form a wiring substrate. In the same manner, a plurality of the wiring substrates are formed. Then, the wiring substrates are laminated and calcined. Another example of the wiring substrate using the photosensitive glass substrate includes a build-up multilayer wiring substrate (see, Japanese Unexamined Patent Application Publication No. 2001-44639 (paragraph numbers [0030] to [0084], and FIGS. 1 to 6)). The build-up multilayer wiring substrate is formed as follows. That is, a conductive film is formed on a through-hole inner wall and a wiring using a plating method. Then, a resin insulating material is formed in the through-hole inside and between the wirings after the conductive film formation.
The wiring substrate for mounting electronic parts is required to have the following conditions. First, since a calcination temperature of an inorganic jointing paste commonly used in jointing electronic parts and a wiring substrate may be as extremely high as 400° C. or more, the substrate must have high thermal resistance. Secondly, the wirings must be densely formed for mounting many small electronic parts, particularly, many ultrasmall ones using the MEMS. Thirdly, the wirings must be formed on the substrate front and rear surfaces for improvement in mounting density.
In a wiring substrate using a photosensitive glass substrate, when using as a core substrate of the wiring substrate a glass substrate having high thermal resistance, a problem in thermal resistance as the wiring substrate can be avoided. However, in the case of filling of a through-hole with conductive paste or formation of wirings by a screen printing method, there may arise a problem that a void is generated in a conductive part formed within the through-hole or minute wirings are unable to be densely formed. Therefore, there are many cases of using a glass substrate having high thermal resistance as well as of forming a through-hole inside conductive part or wirings using the photolithographic method or plating method to cope with thermal resistance as well as miniaturization and density growth. However, in the case of thinly forming a conductive film on a through-hole inner wall, for example, by a plating method and then further filling the through-hole inside with a resin, there arises a problem that even if using a glass substrate having high thermal resistance, the thermal resistance as the whole wiring substrate is reduced. These problems similarly occur both in forming a multilayer wiring substrate and in forming a single layer wiring substrate serving also as a fundamental structure of the multilayer wiring substrate.